The present invention relates to a printed wiring board for a semiconductor plastic package. More specifically, it relates to a printed wiring board for a chip scale package (CSP) formed of a semiconductor chip mounted on a small-sized printed wiring board having almost the same size as the semiconductor chip, and particularly, it relates to a printed wiring board for a very thin ball grid array (BGA) type plastic package.
The printed wiring board as an end product of the present invention, with a semiconductor chip on it, is used in/as a micro-controller, an application specific IC (ASIC), a memory, or the like. The above package is connected to a mother board printed wiring board with solder balls and used in an electronic machine or equipment.
A conventional base material for the chip scale package (CSP) is mainly selected from thin sheets formed of a glass epoxy material, a polyimide film material and a ceramic material. In packages formed of these sheets, a solder ball/solder ball distance is 0.8 mm or more, and yet, it is attempted to decrease the thickness, the size and the weight of the packages. In recent years, therefore, solder balls are getting smaller and smaller in diameter, and the solder ball pitch and the line/space distance of a circuit are decreasing. The above tendency causes problems on heat resistance of a substrate and electric insulation of a multi-layered board after water absorption and anti-migration properties.
In a conventional plastic ball grid array (P-BGA) and CSP, the adhesion of solder balls to a base material decreases with a decrease in the size of a solder ball pad, which causes defective products. Further, since a substrate has a small thickness, a printed wiring board inevitably undergoes distortion due to a variability of thickness of solder resists on front and reverse surfaces of a substrate and a difference in residual ratios of copper foils.
It is an object of the present invention to provide a printed wiring board for a CSP, which overcomes the poor adhesion of solder balls to a base material which poor adhesion is caused by a decrease in the size of the solder balls.
It is another object of the present invention to provide a printed wiring board for a CSP in which the distortion of the printed wiring board is decreased and the distortion of a semiconductor plastic package formed by mounting a semiconductor chip on the printed wiring board by wire bonding or flip chip bonding is decreased.
It is further another object of the present invention to provide a printed wiring board for a CSP, which overcomes the degradation of heat resistance, electric insulation after water absorption and anti-migration properties, which degradation is caused by a decrease in the thickness, size and weight of packages.
According to the present invention 1, there is provided a printed wiring board for a semiconductor plastic package, which printed wiring board has, as a substrate for a chip scale package, a double-side copper-clad laminate formed of an insulation layer having a thickness of 0.2 mm or less and having copper foils on both surfaces, one copper foil on one surface and one copper foil on the other surface,
wherein the double-side copper-clad laminate has an upper copper foil-surface and a lower copper foil surface,
the upper copper foil surface has a wire bonding or flip chip bonding terminal for connecting a terminal of a semiconductor chip to said substrate, and has a copper pad in a position where the copper pad can be electrically connected to said wire bonding or flip chip bonding terminal and can be connected to a blind via hole formed in the lower copper surface,
the lower copper foil surface has a solder-balls-fixing pad in a position corresponding to said copper pad,
the solder-balls-fixing pad has at least 2 blind via holes within itself, and
the solder-balls-fixing pad connected to a reverse surface of the copper pad with a conductive material is electrically connected to a conductive material with solder balls which are melted and filled in blind via holes so as to be mounded.
According to the present invention 1, further, there is provided a printed wiring board as described above, in which the insulation layer of the double-side copper-clad laminate is a film to which a thermosetting resin composition containing, as an essential component, a polyfunctional cyanate ester and a prepolymer of said cyanate ester is adhering or a multi-layered board of such films.
According to the present invention 1, further, there is provided a printed wiring board as described above, in which the insulation layer of the double-side copper-clad laminate is a laminated board formed by impregnating a reinforcing substrate with a thermosetting resin composition containing, as an essential component, a polyfunctional cyanate ester and a prepolymer of said cyanate ester, drying the impregnated reinforcing substrate to obtain prepreg sheets and laminate-forming the prepreg sheets.
According to the present invention 2, there is provided a printed wiring board for a semiconductor plastic package, which printed wiring board is formed by providing a copper-clad laminate formed of copper foils and a base material of a 150 xcexcm to 40 xcexcm thick glass fabric impregnated with a thermosetting resin composition, one copper foil on one surface of the substrate and one copper foil on the other surface of the substrate, arranging at least a semiconductor chip bonding terminal, a solder ball connecting pad, a copper foil circuit for connecting a bonding terminal and said pad and a through hole conductive material in the copper-clad laminate to form a circuit board, then, stacking prepreg sheets of glass fabric base material/thermosetting resin on the entire front and reverse surfaces, laminating the resultant set under pressure and under heat, and then removing base material formed of the glass fabric and the thermosetting resin composition on at least part of the surface of the bonding terminal and on at least part of the surface of the solder balls connecting pad, to expose a circuit.
According to the present invention 2, further, there is provided a printed wiring board for a semiconductor plastic package as described above, in which the glass fabric is at least one woven fabric having a thickness of 50xc2x110 xcexcm, a weight of 35 to 60 g/m2 and a gas permeability of 5 to 25 cm3/cm2.sec.
According to the present invention 2, further, there is provided a printed wiring board for a semiconductor plastic package as described above, wherein the thermosetting resin composition is a thermosetting resin composition containing, as an essential component, a polyfunctional cyanate ester and a prepolymer of said cyanate ester.
According to the present invention, there is provided a printed wiring board for a CSP, which is excellent in the adhesion of solder balls to a substrate, and further, which is excellent in properties such as heat resistance, electric insulation after water absorption and anti-migration properties due to the use of the above-described resin.